Embodiments of the inventive concept relate generally to semiconductor memory devices. More particularly, embodiments of the inventive concept relate to systems, devices, and methods for correcting and preventing the read errors in nonvolatile memory devices.
Semiconductor memory devices can be roughly divided into two categories based on whether they retain stored data when disconnected from power. These categories include volatile memory devices, which lose stored data when disconnected from power, and nonvolatile memory devices, which retain stored data when disconnected from power. Because nonvolatile memory devices retain stored data when disconnected from power, they are often used to store data that must be retained even when devices are powered down.
Examples of volatile memory devices include dynamic random access memory (DRAM) and static random access memory (SRAM). Examples of nonvolatile memory devices include electrically erasable programmable read only memory (EEPROM), ferroelectric random access memory (FRAM), phase-change random access memory (PRAM), magnetoresistive random access memory (MRAM), and flash memory.
Flash memory is among the more popular forms of nonvolatile memory due to its relatively high storage capacity, performance, and reliability. Flash memory can currently be found in a wide variety of consumer and industrial devices, such as such as cameras, cell phones, netbooks, portable memory cards, home electronics, network devices, and embedded controllers, to name but a few.
One of the current limitations flash memory is that it tends to wear out after a certain number of program/erase operations. This wearing out typically occurs on a block-by-block basis because flash memory cells are erased a block at a time. A block of flash memory typically wears out through breakdown of oxide layers that separate floating gates from channel regions of memory cells. The breakdown of these oxide layers reduces the memory cells' ability to retain stored charge, which can lead to decreased read margins and read errors in the memory cells.